Charge for Producing Iron-Ore Pellets (Variants)

ABSTRACT

The invention relates to the field of producing iron-ore pellets for blast-furnace smelting. In a first variant, a charge contains iron-ore concentrate and manganese limestone as a binding agent and flux, the ratio of charge components in wt % being as follows: 1.0-5.0 manganese limestone; and the balance iron-ore concentrate. In a second variant, the charge contains iron-ore concentrate, bauxite as a modifying agent, and manganese limestone as a binding agent and flux, the ratio of charge components in wt % being as follows: 1.0-3.5 manganese limestone; 1.2-1.5 modifying additive; and the balance iron-ore concentrate. The invention increases the strength of green and sintered pellets while preserving a high iron content, reduces the softening-melting interval of the pellets in a blast furnace, and simplifies the production of iron-ore pellets.

RELATED APPLICATIONS

This application is a Continuation Application of InternationalApplication PCT/RU2017/000855, filed on Nov. 17, 2017, which in turnclaims priority to Russian Patent Applications RU2016144588, filed Nov.14, 2016, both of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates to the field of producing iron-ore pellets forblast-furnace smelting.

BACKGROUND OF THE INVENTION

There are various compositions of the charge of pellets forblast-furnace smelting. In the production of fluxed pellets, the chargeconsists of iron-ore concentrate, bentonite and fluxingadditives—limestone, chalk or dolomite.

For example, from the USSR Inventor's Certificate No. 692879, a methodis known for producing pellets from concentrates containing 4-10% silicain barren rock, and fluxing the charge to a CaO/SiO₂ ratio of 0.5-1.3 isproduced with the introduction of magnesium oxide in the amount ofproviding a ratio of CaO:MgO=1.5-3.9. After sintering, cooling to atemperature of 700-900° C. is conducted at a speed of 120-240° C./min.

The disadvantage of this composition of the charge is high basicity,accompanied by a decrease in the iron content in the pellets, and theformation of glass in the structure of the pellets, reducing theirstrength.

The closest technical solution to the technical essence and the achievedresult (the closest analogue is the prototype in the first variant) withrespect to the claimed charge in the first variant is the charge forproducing pellets according to the USSR Inventor's Certificate No.800200 containing iron-ore concentrate and a binder in the form oflime-containing material. In order to reduce the cost of metallurgicalprocessing, the charge contains chalky marl with a particle content of2-0 microns 20-80% as a lime-containing material with the followingratio of ingredients, %: chalky marl 3-7, iron-ore concentrate—the rest.

The disadvantage of this solution is the high SiO₂ content in marl,which reduces the iron content in the pellets, the low strength of theraw pellets and the wide temperature range of softening-melting of thepellets in the blast furnace.

The closest technical solution to the technical essence and the achievedresult (the closest analogue is the prototype in the second variant)with respect to the claimed charge in the second variant is the chargefor producing pellets for metallization in the shaft units followed byhot briquetting according to the patent of the Russian Federation No.2202632 for the invention containing iron-ore material, bentonite,limestone and bauxite in the following ratio of components, wt. %: thesum of bentonite and limestone is 0.5-1.0; bauxite—0.4-1.1; iron-orematerial—the rest.

The disadvantage of this charge composition is the low value of thebasicity of the pellets, which determines the wide softening-meltinginterval in the blast furnace.

SUMMARY OF THE INVENTION

The objective of the invention is to develop a charge for the productionof iron-ore pellets, which eliminated the disadvantages of the knowncharges.

The technical result achieved by the invention increase the strength ofgreen and sintered pellets while maintaining a high iron content,reducing the softening-melting interval of the pellets in the blastfurnace, and simplifies the production of iron-ore pellets.

The technical result is achieved due to the fact that in the charge toobtain iron-ore pellets in the first variant, containing iron-oreconcentrate, flux and binder, according to the invention, the chargecontains manganese limestone, intended for use as a binder, and flux,while the ratio of the components of the charge is, wt %:

manganese limestone—(1.0-5.0);

iron-ore concentrate—the rest.

The manganese content in manganese limestone is at least 6%.

In the charge for producing iron-ore pellets in the second variant,containing iron-ore concentrate, flux and binder, according to theinvention, the charge contains bauxite, intended for use as a modifyingadditive, and manganese limestone, intended for use both as a binder andflux, while the ratio of the components of the charge is, wt %:

manganese limestone—(1.0-3.5);

modifying additive—(1.2-1.5);

iron-ore concentrate—the rest.

The manganese content in manganese limestone is at least 6%.

While using charge in both variants, the preservation of a high ironcontent in the pellets is achieved due to a lower SiO₂ content inmanganese limestone.

The increase in the strength of raw pellets in the charge in bothvariants is due to the increased water-physical properties of manganeselimestone.

Increasing the strength of the sintered pellets in the charge in thefirst variant (when the content of manganese limestone is within thelimits stated in the first embodiment) is achieved by increasing thecontent of manganese oxide.

The lower limit of the content of manganese limestone in the charge inthe first variant, that is, 1.0%, is due to its minimum amount capableof providing high strength of green and sintered pellets. With less than1.0% content of manganese limestone in the charge, the strength of greenand sintered pellets decreases below the level that provides strengthwhen using chalky marl. When the content of manganese limestone in thecharge is less than 1%, the effect of manganese oxide on the softeningand melting temperatures is weak.

The upper limit of the content of manganese limestone in the charge inthe first variant, that is, 5%, is due to a decrease in the iron contentin the pellets and the strength of the sintered pellets. With a greaterthan 5.0% content of manganese limestone in the charge, the strength ofthe sintered pellets is reduced due to the formation of glass in theirstructure. Glass formation also leads to a decrease in the softeningtemperature and an increase in the softening-melting range.

In the charge according to the first variant, the decrease in thetemperature range of softening-melting of the pellets is achieved due tothe influence of manganese oxide (when the manganous limestone contentis within the stated limits in the charge according to the firstvariant) on the softening and melting temperatures of the pellets in theblast furnace.

The reduction in the softening-melting range of pellets in the blastfurnace in the charge according to the second variant is achieved due tothe higher content of Al₂O₃ in the pellets and the influence ofmanganese oxide on the softening temperatures and melting of the pelletsin the blast furnace.

An additional decrease in the softening-melting range of pellets in theblast furnace is achieved by modifying Al₂O₃ with bauxite.

The increase in the strength of green pellets in the charge according tothe second variant is due to the increased water-physical properties ofmanganese limestone, and the strength increase of the sintered pellets(when the content of manganese limestone is within the limit statedaccording to the second variant) is simultaneously due to an increase inthe content of manganese oxide, and also due to the formation of thestructure of the brownmillerite mineral in the interaction of manganeselimestone with aluminum oxide Al₂O₃.

The lower limit of the content of manganese limestone in the charge inthe second variant, that is, 1.0%, is due to its minimum amount capableof providing high strength of green and sintered pellets. With less than1.0% content of manganese limestone in the charge, the strength of greenand sintered pellets decreases below the level that provides strengthwhen using bentonite.

The upper limit of the content of manganese limestone in the charge inthe second variant, that is, 3.5%, is due to a decrease in the ironcontent in the pellets and the strength of the sintered pellets.

With a greater than 3.5% content of manganese limestone in the charge,the strength of the sintered pellets is reduced due to the formation ofglass in their structure.

The lower limit of the bauxite content in the charge according to thesecond variant, that is 1.2%, is due to its minimum amount, at which themodifying effect on the softening and melting temperatures in the blastfurnace occurs. With less than 1.2% bauxite content in the mixture, theeffect of Al₂O₃ on the decrease in softening and melting temperatures isweak.

The upper limit of the bauxite content in the charge in the secondvariant, that is, 1.5%, is due to a decrease in the iron content in thepellets. With a greater than 1.5% bauxite content in the charge, theiron content in the pellets decreases.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The test charge for iron-ore pellets was performed in laboratoryconditions. The iron-ore concentrate was used as the iron-ore material,the chemical composition of which is given in table. 1. There are alsocompositions of fluxes and bauxite given there. Bentonite, fluxes andbauxite were ground in a ball mill to a particle size of less than 0.072mm, injected into the concentrate in a predetermined amount, mixed,moistened, and then the pellets were produced in a drum granulator witha particle size of 10-15 mm Raw pellets were tested for strength bydropping from a height of 30 cm. The sintering was performed in a mufflefurnace with a programmable heat treatment mode at a maximum temperatureof 1300° C. After firing and cooling, the pellets were tested forcrushing strength according to GOST 24765-81, the chemical compositionand softening-melting temperatures were determined according to GOST26517-85.

For comparison, the tests were conducted on the charge of theprototypes, respectively, according to the first and second variant. Thetest results are presented in Table 2.

Analysis of the obtained results shows that the claimed charge forproducing iron-ore pellets in both variants ensures the achievement ofthe stated goal of increasing the strength of raw and sintered pelletswhile maintaining a high iron content and reducing the softening-meltinginterval in the blast furnace.

The charge in both variants for obtaining iron-ore pellets compared tothe corresponding prototypes increases the strength of raw pellets from2.2 to 3.5-5.0 drops, the strength of sintered pellets from 250 to313-510 kg/pellet, reduces the softening-melting temperature range from320 to 240-290° C., retains a high iron content in the pellets.

The claimed technique can be implemented in industry with theachievement of the stated technical result.

Simplification of the charge is due to the fact that manganese limestoneis intended for use as a flux and binder (i.e., such a component of thecharge as a binder is not required separately).

As manganese limestone use natural raw materials (manganese ore),characterized by a manganese content of at least 6%.

TABLE 1 The chemical composition of the charge components, % ComponentsFe FeO Fe₂O3 CaO MgO SiO₂ AL₂O3 MnO LOI Iron-ore concentrate 67.49 28.7064.52 0.22 0.51 5.50 0.19 0.03 0.27 Bentonite — — 1.50 1.00 0.50 60.0036.90 — — Manganese limestone 0.84 — 1.20 40.50 0.77 8.70 3.10 9.9135.75 Bauxite 14.04 — 20.06 0.79 0.75 8.70 40.87 — 24.90 Chalky marl1.12 — 1.60 44.40 0.70 14.50 3.50 — 35.40 Limestone 0.18 — 0.26 54.20.71 1.28 0.34 0.01 42.50 LOI—loss on ignition

TABLE 2 Test Results The strength of The content in the charge, % rawpellets - The iron Crush strength of Softening-melting ExperimentManganese the number of content in sintered pellets, temperature #Concentrate Bentonite limestone Bauxite drops, times the pellets, %kg/pellet range, ° C.  1- 95.0 — Chalky marl — 2.2 64.95 250 320according 5.0 to the USSR IC No. 800200  2 99.2 — 0.8 — 2.7 66.69 265310  3 99.0 — 1.0 — 3.5 66.60 313 275  4 97.0 — 3.0 — 4.0 65.78 402 260 5 95.0 — 5.0 — 5.0 64.95 366 240  6 94.5 — 5.5 — 6.5 64.75 350 255  7-97.9 0.6 Limestone 1.1 3.0 66.12 260 390 according 0.4 to patent No.2,202,632  8 98.1 — 0.8 1.1 2.8 66.33 275 340  9 97.8 — 1.0 1.2 3.966.21 360 290 10 96.7 — 2.0 1.3 4.2 65.77 450 270 11 95.0 — 3.5 1.5 4.565.08 510 265 12 94.4 — 4.0 1.6 4.9 65.84 335 280

What is claimed is:
 1. A charge for producing iron-ore pellets, thecharge comprising an iron-ore concentrate, a flux and a binder, thecharge comprising manganese limestone serving as the binder and theflux, wherein a ratio of components of the charge is, wt %: manganeselimestone—(1.0-5.0); iron-ore concentrate—the rest.
 2. The charge ofclaim 1, wherein a manganese content in the manganese limestone is atleast 6%.
 3. A charge for producing iron-ore pellets, the chargecomprising an iron ore concentrate, a flux and a binder, the chargecomprising a bauxite serving as a modifying additive, and manganeselimestone serving as the binder and the flux, wherein a ratio ofcomponents of the charge is, wt %: manganese limestone—(1.0-3.5);modifying additive—(1.2-1.5); iron-ore concentrate—the rest.
 4. Thecharge of claim 3, wherein a manganese content in the manganeselimestone is at least 6%.